Process of forming electric resistance heating elements



July 25, 1933. E. L. WIEGAND 1,919,816

PROCESS OF FORMING ELECTRIC RESISTANCE HEATING ELEMENTS Filed Dec. 11, 1929 Y Patented July 25, 1933 UNITED STATES PTE'F FFIE EDWIN L. 'WIEGAND, 0F PITTSBURGH, PENNSYLVANIA Application filed December 11, 1929. Serial No. 413,181.

This invention relates to a process of opening therein of the shape shown most forming electric resistance heating elements of the type disclosed in my co-pendlng application Serial No. 283,509, fileddune 7, 5 1928, and of which this application is a continuation in part.

The main object of the invention is to provide a process of forming electrical heatin elements of the character described m which will provide a heating unit which is simple in construction, highly eificlent in operation and at the same time well adapted for production at a low cost.

A further object of the invention is to provide a process of forming an electric heating element having a heating unit which will afford the maximum output of heat at a given temperature and provide ample safeguard against a possible breaking down 0 of the insulation between the resistor and the sheath or cover.

A further object of the invention is to provide a process of forming an electrical heating unit having a heating element consisting of a resistor which is firmly embedded in a mass of granular, electrically insulating, heat conductive, material in such a manner that the resistor will be maintained in spaced relation to the sheath or 0 cover.

Further and more limited objects of the invention will appear as the description proceeds and by reference to the accompanying drawing in which Figs. 1, 2, 3 and 4 are 5 vertical sectional views illustrating the several steps of my process and Fig. 5 is a bottom plan view of the completed heating element.

The heating element consists essentially of a coil of resistance wire embedded in a mass of granular, compacted, electrically insulating, heat conductive, material which in turn is more or less completely encased in a sheet metal sheath. The sheath in the preferred embodiment of the invention is complete and consists of an outer member 1 and an inner member 2 firmly secured together as shown at 3 in Fig. i.

In carrrying out my process, 1 first provide a mold 4 of suitable size having an clearly in Fig. 1. The resistor consists of a wire 6 which is first coiled helically and then wound spirally about a Winding form 7 which is frustate in form. One end of the wire is attached to a bolt 8 whose shank is loosely received in an axial recess 9 provided in the lower face of the form. The Winding form is provided with a volute groove to receve the wire therein. lvhen the exterior of the heating element is to be metal sheathed, the outer member 1 is arranged within the recess in the mold as shown in Fig. 1. The winding form with the resistor wound thereon is placed within the outer sheath member and a layer 1 of granular, electrically insulating, heat conductive material is then poured in to fill the space between the winding form and outer sheath. If desired, a small amount of granular material may be poured into the recess before the winding form is inserted. This layer of material is then compacted by means of a compacting tool 10 having a bore or passageway 11 therein adapted to receive 7E therethrough the projecting end of the resistor. After this layer of material has been firmly tamped, the tamping tool 10 and winding form 7 are removed leaving the wire resistor partially embedded in the layer of granular material.

A second layer 1 of granular material is then introduced. A forming tool 12 is first inserted as shown in Fig. 2. The forming tool 12 has a recess 13 therein adapted to accommodate the bolt 9 to which the lower end of the resistor is connected. This second layer of granular material is compacted and tamped by means of a tamping tool 1 1 having a bore 15 therein to receive the upw per projecting end of the resistor therethrough. These tools are then removed and an asbestos gasket 16 laid on top of the compacted mass 1 in the position shown in Fig. 3. The previously formed sheet metal inner sheath member 2 is then introduced and forced down into the unit to the position shown in Fig. 4. The inner end of the inner sheath member 2 has an opening 17 therein to receive the projecting end of the bolt 9. The inner sheath member 2 also has an overhanging peripheral flange 18 which engages over the gasket 16 and serves to hold the gasket in place. The flange 18 has an opening 19 adapted to receive therethroughthe projecting end of the resistor. It is of course understood that the bolt 9 and the projecting end of the resistor are both insulated from the inner sheath member so as to prevent short circuiting of the resistor. The inner sheath member 2 is forced into the osition shown in Fig. 4 by means of a suita le die. The asbestos gasket 16 is forced down into the unit to the position shown in Fig. 4. The upwardly extending skirt of the outer sheath member 1 is then folded or bent down to the position shown in Fig. 4 and is bent inwardly as shown at 3 to firmly secure the inner sheath member 2 and gasket 16 in place. The peripheral edge of the outer sheath member is flanged outwardly as shown in Fig. 4, and provided with openings 20, 21 and 22 adapted to receive bolts or screws therethrough for securing the heating element to a receptacle. A conductor 23 is connected to the bolt 9 and cooperates with the projecting end 24 of the resistor to provide a means for connecting the heating element with a source of current.

It will now be clear that I have provided a process of forming electrical heating ele ments which will accomplish the objects of the invention as hereinbefore stated.

It will be understood that various changes may be made in the manner of forming the heating element without departing from the spirit of my invention. The asbestos gasket may be in the form of a cup or it may be disk shaped. In some cases, it may be desirable to omit the gasket entirely. While I have here shown a heating element which is completely encased in metal sheathing on both sides, it will be of course understood that one or both faces of the same may be wholly or partly sheathed.

It will therefore be understood that I do not limit myself to any details of design, arrangement, construction except as the same are specifically recited in my several claims. It is therefore understood that my invention is limited only in accordance with the scope of the appended claims.

Having thus described my invention, what I claim is:

1. The method of making a frusto-conical electrical resistance heating element which consists in positioning within a mold a winding form frusto-conical in shape and having a resistor positioned thereon in a plurality of superposed coils, compacting a layer of electrically insulating material about said resistor to partially embed the same, removing the form and compacting a second layer of similar material about said resistor so as to conceal the same and then further compacting the mass thus formed.

2. The method of making a frusto-conical electrical resistance heating element which consists in positioning a resistor in frustoconical shape within a receptacle, compacting a layer of electrical insulating material about said resistor to partially embed the same, removing the resistor positioning means and compacting a second layer of similar material about the resistor to conceal the same and further compacting the mass thus formed.

3. The method of forming a sheathed electrical resistance heating element which is internally hollow and externally tapered which consists in arranging a resistor within a sheath in frustate form, holding the resistor in place and compacting a layer of electrical insulating material about the resistor to partially embed the same, removing the resistor positioning means and com pacting a second layer of electrical insulating material about the resistor so as to cover the same and further compacting the mass.

4. The method of making an electrical resistance heating element which is interiorly hollow and externally tapered which consists in positioning a resistor within a sheath in frustate form, compacting refractory insulating material within the sheath and about the resistor to partially embed the same, removing the resistor positioning means and compacting additional insulating material about the resistor to cover the same, and applying a layer of heat insulating material to the interior of the element.

5. The method of making an electrical resistance heating element which is interiorly hollow and externally tapered which consists in positioning a resistor within a sheath in frustate form, compacting refractory insulating material within the sheath and about the resistor to partially embed the same, removing the resistor positioning means and compacting additional insulating material about the resistor to cover the same, applying a layer of heat insulating material to the interior of the element and thenbending the sheath to secure the heat insulating material in place.

EDWIN L. WIEGAND 

